Recently, there is known a silicon epitaxial wafer manufacturing method in which vapor phase growth of a silicon epitaxial layer (hereinafter, sometimes referred as epitaxial layer) is performed on a front surface of a silicon single crystal substrate (hereinafter, sometimes referred as silicon substrate) to manufacture a silicon epitaxial wafer (hereinafter, sometimes referred as epitaxial wafer).
Such the epitaxial wafer manufacturing method is carried out by supplying silicon material gas onto the front surface of the silicon substrate while heating the silicon substrate arranged in a reaction chamber to perform a vapor phase growth of an epitaxial layer.
More specifically, an epitaxial wafer is manufactured by the following processes.
That is, for example as shown in FIG. 3, first, a silicon substrate is introduced into a reaction chamber which is set to an introduction temperature (for example, about 650° C.) (Step S7).
Next, temperature inside the reaction chamber is heated up (temperature up) to a hydrogen heat treatment temperature (for example, about 1100° C. to 1180° C.) (Step S8) to perform a hydrogen heat treatment, thereby etching an oxide film on a surface of the silicon substrate by hydrogen to remove it (Step S9).
Next, temperature inside the reaction chamber is set to a growth temperature (for example, about 1060° C. to 1150° C.), and silicon material gas (for example, trichlorosilane or the like) is supplied onto a front surface of the silicon substrate. Thereby, the vapor phase growth of an epitaxial layer is performed on the front surface of the silicon substrate to manufacture an epitaxial wafer (Step S10). The hydrogen heat treatment is, specifically, performed before the start of the vapor phase growth.
Next, temperature inside the reaction chamber is cooled down (temperature down) to a withdrawal temperature (for example about 650° C. same as the above described introduction temperature) (Step S11), and the epitaxial wafer is withdrawn from the inside of the reaction chamber (Step S12).
Epitaxial wafers can be manufactured in order by repeating the above described each process (Step S7 to Step S12).
Incidentally, repeating such the manufacturing of an epitaxial wafer would result in gradually depositing silicon deposit inside the reaction chamber, which could be a cause of particles or the like. Particles adhered to a surface of the silicon substrate would have an adverse effect on quality of an epitaxial wafer. Therefore, after repeating manufacture of epitaxial wafers for predetermined times, the etching is performed in the reaction chamber by hydrogen chloride (HCl) gas and a cleaning is performed (HCl cleaning), thereby removing silicon deposit.
That is, specifically, for example as shown in FIG. 4, first, the temperature in the reaction chamber is heated up (temperature up) from the above described withdrawal temperature to an HCl cleaning temperature (for example, about 1190° C.) without introducing a silicon substrate into the reaction chamber (Step S101). Next, a bake is performed (Step S102). Next, hydrogen chloride gas is introduced into the reaction chamber to perform the etching in the reaction chamber for cleaning (performing the HCl cleaning; Step S1031).
When the HCl cleaning is performed, silicon deposit is removed from each portion (susceptor, inside wall of the reaction chamber and the like) inside the reaction chamber, thereby exposing a bare surface of the each portion inside the reaction chamber. However, performing the vapor phase growth in the state that the bare surface of the each portion inside the reaction chamber is exposed would have an adverse effect on quality of an epitaxial wafer due to impurities diffused from the each portion inside the reaction chamber. Therefore, after the HCl cleaning, temperature inside the reaction chamber continues to be set to the growth temperature to introduce silicon material gas into the reaction chamber, thereby coating the surface of the each portion inside the reaction chamber with a silicon thin film (Step S1032). Thereafter, temperature inside the reaction chamber is cooled down to the above described introduction temperature (Step S104) to prepare for the next vapor phase growth. Performing the coating in this manner is successful in suppressing diffusion of impurities from the each portion inside the reaction chamber.
In the above description, the HCl cleaning (Step S1031) and the subsequent coat (Step S1032) are generically named as “etch coat”.
After performing the etch coat (Step S103) or the like, the above described each process (Step S7 to Step S12) is successively repeated to sequentially manufacture an epitaxial wafer.
Incidentally, in a case of performing the vapor phase growth by using a silicon substrate which was subjected to a mirror polishing finished on a rear surface, tarnish is observed on a rear surface of a manufactured epitaxial wafer under light from a collimated light. Especially, such the tarnish is notably observed on an epitaxial wafer manufactured by the first vapor phase growth after the above described etch coat (Step S103 in FIG. 4), which was a cause to lower yield. To put it more concretely, the tarnish has a slight irregularity.
This invention has been accomplished for solving the above described problems, and an object of this invention is to provide a silicon epitaxial wafer manufacturing method capable of suppressing occurrence of tarnish on a rear surface of a manufactured epitaxial wafer even in a case of performing vapor phase growth by using a silicon single crystal substrate which was subjected to mirror polish finished on a rear surface.